Signal processing device, radar apparatus and signal processing program

ABSTRACT

This disclosure provides a signal processing device, which includes a reception signal acquiring module for acquiring reception signals received by a radar antenna, an identifying module for identifying a kind of each reception signal, an extracting module for extracting the reception signal for each kind, and a kind-base signal processing module for performing individual signal processing for each kind of the extracted reception signal.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The application is a divisional of U.S. application Ser. No. 12/941,754filed Nov. 8, 2010, which claims priority under 35 U.S.C. §119 toJapanese Patent Application No. 2009-256499, which was filed on Nov. 9,2009, the entire disclosure of which is hereby incorporated byreference.

TECHNICAL FIELD

The present invention mainly relates to a signal processing device forperforming signal processing to a signal received by a radar antenna.

BACKGROUND

Conventionally, radar apparatuses that transmit an electromagnetic waveby a rotating antenna and receive an echo (reflection wave) from thecircumference are known. Such a radar apparatus is disclosed in JPH11-023707(A) and JP 2003-279641(A), for example.

Appropriate signal processing is applied in a signal processing deviceto the echo signal (hereinafter, referred to as “the reception signal”)received by an antenna. As such signal processing, for example, a gaincontrol, an echo stretch (expansion processing of the echo), echo trailgeneration processing (tracking processing), and scan-to-scancorrelation processing can be used.

Hereinafter, the gain control is briefly described as an example of thesignal processing. That is, the reception signal may include, in manycases, signals unnecessary for an operator. For this reason,conventionally, predetermined signal processing is performed to thereception signal to suppress a signal level of the unnecessary signals(gain control).

The conventional gain control generally reduces the signal level of theunnecessary signals by performing suitable processing for the inputtedreception signal, applies threshold processing, and then outputs theprocessed signal, for example. Here, the threshold processing outputs asignal having the signal level equal to or higher than a predeterminedthreshold level (otherwise, a signal having the signal level below thethreshold level is not outputted). As described above, the signal can beoutputted after the level of unnecessary signals is suppressed by thegain control.

However, the gain control has a disadvantage in which the signals“necessary” for the operator may also be suppressed when the unnecessarysignals are excessively suppressed.

In the meantime, JP H11-023707(A) discloses a configuration in whichonly the reception signals from an ocean area are outputted by usingelectronic nautical chart information. Therefore, the necessaryreception signals (signals from the ocean area) can be certainlyoutputted, thereby suppressing only the unnecessary reception signals(signals from a land area).

However, it is believed that the signals received by the antenna includevarious kinds of signals, such as signals indicating sea surfacereflections, signals indicating rain-and-snow clutters, signalsindicating echoes from other ships, signals indicating echoes from land,and signals indicating echoes from buoys or flag buoys.

In this regard, however, because the method of JP H11-023707(A) onlydistinguishes the ocean areas from the land areas based on theelectronic nautical chart information, it cannot be applied to thecontrol such as applying the gain control only to the sea surfacereflections.

That is, the conventional signal processing device cannot performflexible processing such as selecting an arbitrary kind of receptionsignal to perform the gain control. This is not limited only to the gaincontrol, but the signal processing cannot be performed after thearbitrary kind of the reception signal is selected, also for the echostretch, the echo trail generation processing, and the scan-to-scancorrelation processing, etc.

SUMMARY

The present invention is made in view of the above situations, andprovides a signal processing device that can flexibly perform signalprocessing according to a kind of a reception signal.

According to one aspect of the present invention, a signal processingdevice is provided, which includes a reception signal acquiring modulefor acquiring reception signals received by a radar antenna, anidentifying module for identifying a kind of each reception signal, anextracting module for extracting the reception signal for each kind, anda kind-base signal processing module for performing individual signalprocessing for each kind of the extracted reception signal.

Thereby, suitable signal processing can be performed according to eachkind of the reception signals. Further, because the reception signalsare extracted for each kind, and the individual signal processing isperformed for the corresponding kind, the signal processing can beprevented from affecting other kinds of reception signals. Therefore,flexible signal processing is possible, for example, when performing again control as the signal processing, only arbitrary kinds of thereception signals can be selectively suppressed.

The identifying module may identify at least any one of the kinds of thereception signal, the kinds including a land, a ship, a buoy, a flagbuoy, a sea surface reflection, a rain-and-snow clutter, and a whitenoise.

The signal processing device may further comprise a map informationacquiring module for acquiring map information. The identifying modulemay identify the kind of the reception signal based on the mapinformation.

The identifying module may identify the reception signal indicating aland based on the map information. The kind-base signal processingmodule may perform signal processing, which is different from signalprocessing for other kinds of the reception signals, for the receptionsignal indicating the land.

The signal processing device may further comprise an AIS informationacquiring module for acquiring AIS information. The identifying modulemay identify the kind of the reception signal based on the AISinformation.

The identifying module may identify the reception signal indicating aship based on the AIS information. The kind-base signal processingmodule may perform signal processing, which is different from signalprocessing for other kinds of the reception signals, for the receptionsignal indicating the ship.

The signal processing device may further comprise a sea surfacereflection detecting module for identifying a reception signalindicating a sea surface reflection. The kind-base signal processingmodule may perform signal processing, which is different from signalprocessing for other kinds of the reception signals, for the receptionsignal indicating the sea surface reflection.

The signal processing device may further comprise a rain-and-snowclutter detecting module for identifying a reception signal indicating arain-and-snow clutter. The kind-base signal processing module mayperform signal processing, which is different from signal processing forother kinds of the reception signals, for the reception signalindicating the rain-and-snow clutter.

The signal processing device may further comprise a display processingmodule for synthesizing the reception signals for the kinds, for whichthe signal processing is carried out by the kind-base signal processingmodule, to generate a radar image.

The signal processing device may further comprise a layer storage modulefor storing the reception signals, for each kind for which the signalprocessing is carried out by the kind-base signal processing module, inlayers prepared for the kinds, and a display layer selecting module forselecting some or all layers from the layers for the kinds based on aninput from the exterior. The display processing module may synthesizethe layers, which are selected by the display layer selecting module, togenerate the radar image.

According to another aspect of the present invention, a signalprocessing device is provided, which includes a reception signalacquiring module for acquiring reception signals received by a radarantenna, an identifying module for identifying a kind of each receptionsignal, an identifier granting module for giving an identifier to thereception signal according to the kind of the reception signal, anextracting module for extracting the reception signal for each kindbased on the identifier, and a kind-base signal processing module forperforming individual signal processing for each kind of the extractedreception signal.

Thus, by giving the identifier to each reception signal, the receptionsignal can be easily extracted for each kind by the extracting module.

According to another aspect of the present invention, a radar apparatusis provided, which includes any one of the above signal processingdevices, and a radar antenna module for transmitting an electromagneticwave, receiving a reflection wave, and outputting a reception signalcorresponding to the received reflection wave to the signal processingdevice.

This radar apparatus can flexibly perform the signal processingaccording to the kind of the reception signal.

According to another aspect of the present invention, a signalprocessing program for causing a signal processing device to executeprocessing is provided. The processing includes identifying a kind of areception signal received by a radar antenna, extracting the receptionsignal for each kind, and performing individual signal processing foreach kind of the extracted reception signal.

Thereby, suitable signal processing can be performed according to thekind of the reception signal. Because the reception signal is extractedfor each kind, and the individual signal processing is performed for thekind, the signal processing can be prevented from affecting other kindsof reception signals.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is illustrated by way of example and not by wayof limitation in the figures of the accompanying drawings, in which thelike reference numerals indicate like elements and in which:

FIG. 1 is a block diagram showing a configuration of a ship radarapparatus according to an embodiment of the present invention;

FIG. 2A is a schematic diagram of a radar image displayed on a displaymodule in the ship radar apparatus of this embodiment, and FIG. 2B is aschematic diagram of a radar image in a conventional radar apparatus;

FIG. 3 is a conceptual diagram showing a reception signal beingextracted for each kind; and

FIG. 4 is a conceptual diagram showing a generation of a radar image bysynthesizing layers.

DESCRIPTION OF EMBODIMENT

Next, an embodiment of the present invention is described with referenceto the appended drawings. FIG. 1 is a block diagram showing aconfiguration of a ship radar apparatus 1 of this embodiment.

The ship radar apparatus 1 includes an antenna unit 2 (radar antennamodule) provided with a radar antenna 11 and a radar transceiving module12, and a radar indicator 3 (signal processing device).

The ship radar apparatus 1 is configured as what is called a pulse radarapparatus. That is, the radar antenna 11 transmits a pulse-shapedelectric wave having a strong directivity, and receives an echo(reflection wave) produced by the pulse-shaped electric wave reflectedon a target object (a source of the echo) and returned to the antenna.The radar antenna 11 repeatedly transmits and receives the electric wavewhile revolving in a horizontal plane at a predetermined revolvingspeed. With the above configuration, each scan is performed in thehorizontal plane for 360° centering on a ship, which is equipped withthe apparatus (hereinafter, referred to as “the ship” or “the shipconcerned”), to acquire the situation of the surrounding echo sources.

The reception signal received by the radar antenna 11 is sampled by anA/D conversion module (not illustrated) which the radar transceivingmodule 12 has, converted into a digital signal, and inputted into theradar indicator 3. In the following description, each sample value asthe result of sampling the reception signal may be referred to as“reception data.”

The radar indicator 3 mainly includes a reception signal acquiringmodule 13, a control module 14, a display processing module 15, and adisplay module 16.

The reception signal acquiring module 13 is an interface for taking thereception signal from the outside into the radar indicator 3 (forexample, a connector). The digital reception signal acquired by thereception signal acquiring module 13 is outputted to the control module14.

The control module 14 performs predetermined signal processing to thereception signal (described later in detail). Therefore, in thisembodiment, the radar indicator 3 functions as the signal processingdevice. Then, the display processing module 15 generates a raster imageindicating the situation of the echo sources around the ship concerned(radar image), and outputs it to the display module 16. Therefore, inthis embodiment, the radar indicator 3 also functions as a radar imagegenerating device.

Typically, the display module 16 is configured as a liquid crystaldisplay in which a color indication is possible to display the radarimage. With the above configuration, the situation of the echo sourcesaround the ship concerned acquired by the radar antenna 11 can bedisplayed on the display module 16.

An example of the radar image displayed on the display module 16 isshown in a schematic diagram of FIG. 2A. As shown in FIG. 2A, echoimages which indicate ships 91, buoys 92, lands 93, rain-and-snowclutters 95 and the like are displayed centering on a position 90 of theship concerned (hereinafter, it may also be referred to as “the shipposition”) in the radar image. Therefore, an operator of the ship radarapparatus 1 can travel the ship safely by checking the radar imagedisplayed on the display module 16, even in a situation where it isdifficult for the operator to check the surroundings by naked eyes atnight, for example.

In order to show the comparison with the radar image by the ship radarapparatus 1 of this embodiment, an example of a radar image by aconventional radar apparatus is shown in a schematic diagram of FIG. 2B.As shown in FIG. 2B, the conventional radar apparatus displays seasurface reflections 94 which cause an unnecessary echo image. Inaddition, because the buoys 92 and the like cause a low echo signallevel and echo images produced by the buoys are small, the operator mayoverlook the images. In addition, the radar image of the conventionalradar apparatus causes a problem in which it is difficult for theoperator to grasp the exact outline shapes (coastlines) of the lands 93.One of the lands 93 is buried in the echo image of the rain-and-snowclutter 95, and it makes even more difficult to grasp the land shape.

In such a case, if the gain control is performed by the conventionalradar apparatus to suppress the sea surface reflections, therain-and-snow clutters and the like as already described, it alsosuppresses necessary signals. Specifically, if the gain control isperformed to suppress the sea surface reflections and the rain-and-snowclutters by the conventional radar apparatus, another problem is causedin which the weak echo signal images, such as the buoys 92 in FIG. 2B,are no longer displayed in the radar image.

On the other hand, as shown in FIG. 2A, this embodiment can avoid theecho images of the sea surface reflections from being displayed. Thatis, it is possible to suppress only the unnecessary signals (sea surfacereflections), leaving the necessary signals (ships, buoys, lands, etc.).Because the echo images of the rain-and-snow clutters are importantinformation to travel avoiding the rain clouds, they are displayed whiletheir signal levels are suppressed, without being completely suppressedlike the sea surface reflections (in the figure, the strengths of thesignal levels are expressed by intervals of hatchings). As shown in FIG.2A, like the buoys 92, echo images which are small and hard to see canbe displayed enlarged (comparing with the conventional radar image ofFIG. 2B). Further, the outlines of the lands 93 are emphasized bythickening the coastlines and the areas of the lands are filled withcolor (in this figure, filled with hatchings). Therefore, the outlineshapes of the lands 93 can be correctly grasped. As described above, theradar apparatus of this embodiment is configured to flexibly adjust theecho images according to the kinds of echo sources.

Next, the configuration for adjusting the echo images for every kind isdescribed in detail.

First, a configuration of the control module 14 is described. Thecontrol module 14 is constituted with hardware, such as a CPU, a RAM anda ROM (not illustrated), and software, such as a signal processingprogram stored in the RAM. The signal processing program includes acommon signal processing step, an identifying step, an extracting step,a header insertion processing step, a kind-base signal processing step,a scan-to-scan correlation processing step, and a statistical processingstep, etc. By the hardware and the software cooperating, the controlmodule 14 can function as a common signal processing module 17, a kindidentification processing module 18, a header insertion processingmodule 19, a kind-base signal processing module 20, a scan-to-scancorrelation processing module 21, and a statistical processing module22, etc. Hereinafter, these components are described in detail withreference to the block diagram of FIG. 1.

The common signal processing module 17 performs processing such as noiseremoval and interference removal for the reception signal inputted fromthe reception signal acquiring module 13. The processing of the commonsignal processing module 17 corresponds to the common signal processingstep of the signal processing program. The reception signal for whichthe processing such as the noise removal is applied is outputted to thekind identification processing module 18.

The kind identification processing module 18 performs processing foridentifying the kind of the reception signal, for the reception signaloutputted from the common signal processing module 17. In thisembodiment, the processing for identifying the kind of reception signalis performed for each of the reception data. More specifically, theprocessing performed by the kind identification processing module 18identifies the kind of echo source on which a signal is reflected, wherethe signal is sampled to produce each reception data. The processing ofthe kind identification processing module 18 corresponds to theidentifying step of the signal processing program.

Here, in the case of the ship radar apparatus 1 of this embodiment, thereception signal received by the radar antenna 11 may include a signalindicating the echo based on the sea surface reflection, a signalindicating the echo based on the rain-and-snow clutter, a signalindicating the echo from another ship, a signal indicating the echo froma land, a signal indicating the echo from a buoy or a flag buoy, and anecho of a side lobe. Thus, because two or more possibilities may beconsidered as the kind of reception signal, the kind of reception signalis identified by using the combination of two or more methods in thisembodiment.

Broadly, the method of identifying the kind of reception signal can bedivided into two methods in this embodiment: a method of identifying thekind by using information other than the reception data; and a method ofidentifying the kind based on information obtained by applyingpredetermined processing to the reception data.

First, the method of using the information other than the reception datais described. In this embodiment, AIS information and map informationare mainly used as the information other than the reception data. Forthis reason, an AIS receiver 23, a GPS receiver 24, an azimuth directionsensor 25, and a map information holding module 26 are connected withthe ship radar apparatus 1.

The AIS receiver 23 receives AIS signals transmitted from other ships.The AIS (Universal Shipborne Automatic Identification System) is asystem for transmitting positional information, traveling informationand the like on a ship to the circumference by wireless communications,and, by receiving similar information from other ships, the system canbe acquired information on the positions and the like of other ships(AIS information). The AIS receiver 23 outputs the received AISinformation to the ship radar apparatus 1. An AIS information acquiringmodule 27 which the ship radar apparatus 1 equips acquires the AISinformation.

The GPS receiver 24 receives GPS signals from GPS Satellites to acquireinformation on the position of the ship concerned (absolute positionbased on the earth), and outputs it to the ship radar apparatus 1. A GPSinformation acquiring module 28 which the ship radar apparatus 1 equipsacquires the information on the ship position.

The azimuth direction sensor 25 acquires the bow direction of the shipconcerned (absolute bearing based on the earth), and outputs it to theship radar apparatus 1. An azimuth direction information acquiringmodule 29 which the ship radar apparatus 1 equips acquires theinformation on the bow direction.

The map information holding module 26 is a storage medium or an externalinstrument that stores the map information (electronic nautical chart orcoastline data). A map information acquiring module 30 which the shipradar apparatus 1 equips reads out the map information from the mapinformation holding module 26 to acquire the contents stored therein.

The information acquired by the AIS information acquiring module 27, theinformation acquired by the GPS information acquiring module 28, theinformation acquired by the azimuth direction information acquiringmodule 29, and the information acquired by the map information acquiringmodule 30 are inputted into the kind identification processing module18, respectively.

The kind identification processing module 18 identifies whether eachreception data indicates an echo from a ship based on the AISinformation acquired by the AIS information acquiring module 27.Specifically, it is as follows.

It is well known that, in a pulse radar apparatus like the ship radarapparatus 1, a distance r to an echo source (a ship, a land, etc.) canbe acquired based on a time period from the transmission of the electricwave to the reception of the echo. Based on the direction of the antennawhen the echo is received, an azimuth direction θ of the echo sourceseen from the ship concerned can be acquired. That is, the position ofthe echo source corresponding to each reception data can be acquired bypolar coordinates (r, θ). In the meantime, positions of other shipssurrounding the ship concerned can be acquired based on the AISinformation.

Therefore, the position (r, θ) of the echo source corresponding to eachreception data is compared with the positions of other ships(surrounding ships) acquired based on the AIS information to identifywhether the reception data indicates an echo from a ship (whether thekind of the reception data is a ship or not).

Note that the position of the echo source acquired by the radarapparatus is relative positional information centering on the shipconcerned. On the other hand, the positions of other ships acquiredbased on the AIS information are absolute positional information basedon the earth. Therefore, in order to compare the both, the absolutepositional information of other ships based on the AIS need to beconverted into the relative positional information centering on the shipconcerned. For this reason, the kind identification processing module 18compares the absolute positional information of other ships acquiredbased on the AIS information with the relative positional information ofthe echo source acquired by the radar apparatus, after the absolutepositional information is converted into the relative positionalinformation using the GPS information and the azimuth directioninformation.

The kind identification processing module 18 identifies whether eachreception data indicates an echo from a land based on the mapinformation acquired by the map information acquiring module 30.Specifically, it is as follows.

The map information includes data that expresses information on theshape, the position and the like of the land by the absolute coordinatesbased on the earth. Therefore, the kind identification processing module18 compares the position of the echo source corresponding to eachreception data with the information on the position and shape of theland acquired based on the map information to identify whether thereception data indicates the echo from the land (whether the kind of thereception data is the land or not). Because the information included inthe map information is expressed by the absolute coordinates based onthe earth, the kind identification processing module 18 compares theposition and shape of the land acquired based on the map informationwith the positional information of the echo source acquired by the radarapparatus, after converting the position and shape of the land into therelative information similar to the case of the AIS information.

Next, the method of identifying the kind of reception signal based onthe information acquired by applying predetermined processing to thereception data is described. In this embodiment, as the method ofidentifying the kind, a method of identifying the kind based on theprocessed result of the scan-to-scan correlation processing module 21, amethod of identifying the kind based on the processed result of thestatistical processing module 22, and a method of identifying the kindby recognizing an appearing pattern of the signal are adopted.

The scan-to-scan correlation processing module 21 performs scan-to-scancorrelation processing to the reception data for which the noise removaland the like is applied by the common signal processing module 17. Theprocessing of the scan-to-scan correlation processing module 21corresponds to the scan-to-scan correlation processing step of thesignal processing program.

Because the scan-to-scan correlation processing is known in the art,detailed description thereof is omitted herein. However, it isprocessing in which a correlation between the latest reception signaland the past reception signal is taken to suppress signals which vary atrandom with time (signals having low correlations with the pastreception signals), leaving signals stably detected with time (signalshaving high correlations with the past reception signals). Here, thesignals stably detected with time include the echoes from a ship, abuoy, and a land, etc. On the other hand, the signals varying at randomwith time include the echoes based on sea surface reflections.Therefore, only the signals based on the sea surface reflections can besuppressed by performing the scan-to-scan correlation processing for thereception signals.

The reception signal for which the scan-to-scan correlation processingis applied is outputted to the kind identification processing module 18from the scan-to-scan correlation processing module 21. As describedabove, because only the sea surface reflection is suppressed for thereception signal after the scan-to-scan correlation processing, the kindidentification processing module 18 checks the reception data for whichthe signal level is suppressed to detect the reception data indicatingthe echo based on the sea surface reflection. By this method, the kindidentification processing module 18 identifies whether each receptiondata indicates the sea surface reflection (whether the kind of receptiondata is the sea surface reflection or not). As described above, becausethe scan-to-scan correlation processing module 21 performs processingfor identifying the reception data indicating the sea surfacereflection, it can be said that the scan-to-scan correlation processingmodule 21 is a sea surface reflection detecting module.

Among the reception signals after the scan-to-scan correlationprocessing, a signal for which the signal level is not suppressed is thesignal which is stably detected with time (a signal indicating the echofrom a ship, a buoy or a flag buoy, a land, etc.). Here, the receptiondata indicating the echo from a ship and the reception data indicatingthe echo from a land can be discriminated by the method alreadydescribed. Therefore, the kind identification processing module 18identifies reception data which is identified as not being a ship nor aland as reception data indicating a buoy (or a flag buoy), among thereception data for which the signal level is not suppressed by thescan-to-scan correlation processing.

The statistical processing module 22 acquires statistical informationfor the reception signal for which the noise removal and the like isapplied by the common signal processing module 17. The processed resultof the statistical processing module 22 is outputted to the kindidentification processing module 18. The kind identification processingmodule 18 identifies whether each reception data indicates arain-and-snow clutter based on the statistically processed resultoutputted from the statistical processing module 22 (whether the kind ofreception data is the rain-and-snow clutter or not). As described above,because the statistical processing module 22 performs the processing foridentifying the reception data indicating the rain-and-snow clutter, itcan be said that the statistical processing module 22 is a rain-and-snowclutter detecting module.

Hereinafter, the above-mentioned processing is described briefly. Thatis, the reception signal indicating the echo based on the rain-and-snowclutter has a certain tendency. Therefore, the statistical informationof the signal level of the reception data contained within a certaindistance range is extracted, and if the statistical information is inagreement with the pattern indicated by the echo based on therain-and-snow clutter, the kind identification processing module 18determines that the reception data within the distance range indicatesthe echo based on the rain-and-snow clutter (For example, a histogram ofthe signal level of the reception data contained within a certaindistance range is obtained, and if the histogram indicates apredetermined pattern, the reception data within the distance range isdetermined to indicate the echo based on the rain-and-snow clutter).

Echoes of side lobes appear by a predetermined pattern near an echo of amain lobe. The kind identification processing module 18 recognizeswhether each reception data follows the appearing pattern to identifywhether the reception data indicates the echo of the side lobe.

With the above configuration, the kind identification processing module18 can identify which echo each reception data indicates among the echobased on the sea surface reflection, the echo based on a rain-and-snowclutter, the echo from a ship, the echo from a land, the echo from abuoy (or a flag buoy), and the echo of a side lobe. That is, because thekind identification processing module 18 identifies the kind of eachreception data, it can be said that the kind identification processingmodule 18 identifies the kind of reception signal. For example, if it israining on a land, one reception data may indicate both the echo basedon the rain-and-snow clutter and the echo from the land. Therefore, onereception data may be classified into two or more kinds. The identifiedresult of the kind of each reception data by the kind identificationprocessing module 18 is outputted to the header insertion processingmodule 19.

The header insertion processing module 19 (identifier granting module)gives header information (identifier) indicating the kind of eachreception data. The processing of the header insertion processing module19 corresponds to the header inserting step of the signal processingprogram.

The header information is preferred to be configured as a bit flag for 6bits, for example. For instance, the 0th bit is set to a land flag, the1st bit to a ship flag, the 2nd bit to a buoy/flag-buoy flag, the 3rdbit to a sea surface reflection flag, the 4th bit to a rain-and-snowclutter flag, and the 5th bit to a side lobe flag. In this case, headerinformation “000010” is given to the reception data indicating the echofrom a ship (here, the right end bit is set to the 0th bit). Inaddition, header information “010001” may be given to the reception dataindicating both the echo from the land and the echo based on therain-and-snow clutter, for example.

An example in which the header information is given to the receptiondata is shown in the top of FIG. 3. In the figure, an example waveformof the reception signals which are received during one sweep (operationfrom a single transmission of the pulse-shaped electric wave to areception of the echo), where the vertical axis indicates the signallevel and the horizontal axis indicates the distance to the echo source.Although the header information only on a part of the reception signalis shown in FIG. 3, the header information is given in fact to everyreception data for which the reception signal is sampled. The receptiondata to which the header information is given is outputted to thekind-base signal processing module 20.

The kind-base signal processing module 20 includes a land signalprocessing module 40 for performing signal processing to the receptionsignal indicating the echo from a land, a ship signal processing module41 for performing signal processing to the reception signal indicatingthe echo from a ship, a buoy/flag-buoy signal processing module 42 forperforming signal processing to the reception signal indicating the echofrom a buoy (or a flag buoy), a sea surface reflection signal processingmodule 43 for performing signal processing to the reception signalindicating the echo by a sea surface reflection, and a rain-and-snowclutter signal processing module 44 for performing signal processing tothe reception signal indicating the echo by a rain-and-snow clutter.Because the echoes of the side lobes are unnecessary fake images, thesignal processing to the reception signal indicating the echo of theside lobe is not carried out.

When the reception data with the header information is inputted, thekind-base signal processing module 20 acquires the kind of the receptiondata based on the header information, and outputs the reception data tothe signal processing module corresponding to the kind among the signalprocessing modules 40-44. For example, because the reception data wherethe 0th bit of the bit flag is “1” (land flag) is reception dataindicating the echo from the land, it is outputted to the land signalprocessing module 40. For example, because the reception data where the1st bit of the bit flag is “1” (ship flag) is reception data indicatingthe echo from the ship, it is outputted to the ship signal processingmodule 41.

Because the above processing is carried out for all the reception data,if the whole waveform of the reception signals is considered, receptionsignals classified by the kinds are extracted from the originalreception signals, and individual signal processing is performed foreach of the reception signals classified by the kinds. This processingis conceptually shown in FIG. 3. As shown in FIG. 3, from the receptionsignals shown in the top (first row) (reception signals to which theheader information is given), the reception signal indicating the echofrom the land, the reception signal indicating the echo from the ship,and the reception signal indicating the echo from the buoy (or the flagbuoy), the reception signal indicating the echo based on the sea surfacereflection, and the reception signal indicating the echo based on therain-and-snow clutter are extracted. The extracted reception signals areinputted into the respective signal processing modules corresponding tothe kinds of the reception signals. Thus, the kind-base signalprocessing module 20 can be said that it is an extracting module forextracting a signal for every kind Note that the processing of thekind-base signal processing module 20 as the extracting modulecorresponds to the extracting step of the signal processing program.

Hereinafter, signal processing to be performed by each of the signalprocessing modules 40-44 is described in detail. Note that theprocessing of the signal processing modules 40-44 corresponds to thekind-base signal processing step of the signal processing program.

Because only the reception data indicating the echo from the land isinputted to the land signal processing module 40, processing peculiar tothe echo from the land can be performed. Specifically, the land signalprocessing module 40 performs processing for amplifying the signal levelof the reception data from an area corresponding to a coastline, forexample. Thus, because the echo image for which the coastline isemphasized can be displayed on the radar image, the operator cancorrectly grasp the outline shape of the land (coastline).Alternatively, the land signal processing module 40 may performprocessing in which the signal level of the inputted reception data isset to be constant. Thereby, because the echo image of the land area isdisplayed so that it is uniformly painted out on the radar image, theoperator can easily recognize the existence of the land.

Because only the reception data indicating the echo from the ship isinputted to the ship signal processing module 41, it can performprocessing peculiar to the echo from the ship. Specifically, the landsignal processing module 40 performs processing for raising the signallevel of the inputted reception data, for example (raising a gain).Thereby, the echo image indicating the echo from the ship can bedisplayed so as to be emphasized on the radar image. Alternatively,processing for sharpening the outline of the echo image may beperformed.

Because only the reception data indicating the echo from the buoy or theflag buoy is inputted to the buoy/flag-buoy signal processing module 42,it can perform processing peculiar to the echo from the buoy (or theflag buoy). Specifically, the buoy/flag-buoy signal processing module 42performs echo expansion (echo stretch) processing, for example. Thereby,even if it is a small target object like the buoy or the flag buoy, theecho image can be displayed large in size so that the operator is easyto see it on the radar image.

Because only the reception data indicating the echo based on the seasurface reflection is inputted to the sea surface reflection signalprocessing module 43, it can perform processing peculiar to the echobased on the sea surface reflection. Specifically, the sea surfacereflection signal processing module 43 performs processing for loweringthe signal level of the reception data, for example (processing forlowering the gain). Thereby, it can prevent the sea surface reflectionsfrom being displayed on the radar image.

Because only the reception data indicating the echo based on therain-and-snow clutter is inputted to the rain-and-snow clutter signalprocessing module 44, it can perform processing peculiar to thereception signal indicating the echo based on the rain-and-snow clutter.Specifically, the rain-and-snow clutter signal processing module 44performs processing for lowering the signal level of the reception data,for example (processing for lowering the gain). Thereby, it can preventthe rain-and-snow clutters from being displayed on a radar image.Alternatively, the rain-and-snow clutter signal processing module 44 mayperform the processing for raising the gain according to an operator'sselection. Thereby, because an area where rain is falling can be clearlydisplayed on the radar image, it can also support the needs to travel onthe course where rain clouds are avoided.

As described above, because the signal processing is selectivelyperformed according to the kind of reception data, one signal processingdoes not affect the reception data of other kinds For example, even ifthe processing for lowering the gain is performed to the reception dataindicating the echo based on the sea surface reflection, the gain of theother kind of the reception data is not lowered. Therefore, because thesignal processing which is independent for each kind of the receptiondata can be performed, the echo image can be flexibly adjusted, and,thereby, the radar image where information necessary to the operator canbe generated to be clearly displayed.

Next, a configuration for generating the radar image is described.

Each of the signal processing modules 40-44 outputs the signal-processedreception data to an image memory 31, after performing the signalprocessing described above. Thereby, the image memory 31 stores a rasterimage indicating the situation of the echo sources around the shipconcerned.

Although the method of generating the raster image based on thereception data is well known in the art, it is described briefly below.As described above, the position of the echo source indicated by thereception data is acquired by polar coordinates. On the other hand, theposition of each pixel of the raster image is expressed by rectangularcoordinates. For this reason, when outputting the reception data to theimage memory, the position of the echo source expressed by the polarcoordinates is converted into rectangular coordinates, and a pixeladdress corresponding to the position is specified and outputted.Thereby, an echo image is plotted at suitable pixels in the raster imagestored in the image memory. Then, this processing is performed for thereception data for one revolution of the radar antenna to generate theraster image indicating the situation of the echo sources around theship concerned.

The image memory 31 can store two or more raster image data. Herein,each of the two or more of image data may be called a “layer.” The layeris prepared for every kind of the reception signal. That is, the imagememory 31 includes a land drawing layer storage module 50 for storing aland layer, a ship drawing layer storage module 51 for storing a shiplayer, a buoy/flag-buoy drawing layer storage module 52 for storing abuoy layer (or a flag buoy layer), a sea surface reflection drawinglayer storage module 53 for storing a sea surface reflection layer, anda rain-and-snow clutter drawing layer storage module 54 for storing arain-and-snow clutter layer.

Here, the “land layer” is a raster image generated based on thereception data outputted from the land signal processing module 40. The“ship layer” is a raster image generated based on the reception dataoutputted from the ship signal processing module 41. The “buoy layer (orflag buoy layer)” is a raster image generated based on the receptiondata outputted from the buoy/flag-buoy signal processing module 42. The“sea surface reflection layer” is a raster image generated based on thereception data outputted from the sea surface reflection signalprocessing module 43. The “rain-and-snow clutter layer” is a rasterimage generated based on the reception data outputted from therain-and-snow clutter signal processing module 44.

As described above, because the reception data for which each of thesignal processing modules 40-44 performs the signal processing isobtained by extracting only the specific kind of reception data, thesignal-processed reception data outputted from each of the signalprocessing modules 40-44 contains only the specific kind of receptiondata, respectively. Further, the reception data outputted from each ofthe signal processing modules 40-44 is obtained by performing the signalprocessing according to the kind of the reception signal concerned.Accordingly, each of the layer storage modules 50-54 for every kindstores the raster image for which the echo image is adjusted for eachkind (refer to the left-hand side of FIG. 4). Note that, as describedabove, because the raster image can be finally generated by executingthe signal processing program of this embodiment, it can be also saidthat the signal processing program of this embodiment is a radar imagegeneration program.

For example, the land layer stored in the land drawing layer storagemodule 50 contains only the echo image indicting the land, and,moreover, in the echo image, the coastline area is emphasized by thesignal processing of the land signal processing module 40. Similarly,for example, the buoy layer (or the flag buoy layer) stored in thebuoy/flag-buoy drawing layer storage module 52 contains only the echoimage indicating the buoy or the flag buoy, and, moreover, the echoimage is expanded by the signal processing of the buoy/flag-buoy signalprocessing module 42. Thus, the echo image contained in each layer isappropriately adjusted according to the kind of the echo image.

A display layer selecting module 32 is inputted with a display layerselection signal indicating a layer to be displayed which is specifiedby the operator among the layers stored in the layer storage modules50-54. The display layer selecting module 32 selects some or all layersaccording to the display layer selection signals, reads out the selectedlayers from the image memory 31, and outputs them to the displayprocessing module 15. The display processing module 15 stacks(superimposes) the respective layers outputted from the display layerselecting module 32, and performs processing for generating a singleraster image (radar image). The radar image generated by the displayprocessing module 15 is transmitted to and displayed on the displaymodule 16.

FIG. 4 conceptually shows processing for generating the radar image. InFIG. 4, the case where the operator sets such that the sea surfacereflections are not displayed on the radar image is shown. In this case,the display layer selecting module 32 reads out layers from the layerstorage modules 50, 51, 52, and 54 other than the sea surface reflectiondrawing layer storage module 53, and outputs them to the displayprocessing module 15. Thereby, because the sea surface reflection layeris not outputted to the display processing module 15, a radar imagewithout containing the echo images indicating the sea surfacereflections can be generated by performing the processing for stackingthe layers by the display processing module 15.

Note that the configuration for superimposing two or more images anddisplaying the superimposed image on a display module is disclosed in JP2003-279641(A) described above, for example. However, JP 2003-279641(A)uses a radar image with a single layer. Therefore, unlike thisembodiment, it cannot perform the processing for not selectivelydisplaying the echo image of the specific kind. In this regard, in thisembodiment, because the ship radar apparatus 1 divides the radar imageinto two or more layers, it is possible to select “display/non-display”for every layer.

Further, the echo images are adjusted according to the respective kindsfor the layers outputted from the display layer selecting module 32 (theland layer, the ship layer, the buoy layer (or the flag buoy layer), andthe rain-and-snow clutter layer). Therefore, by superimposing the layersin the display processing module 15, the radar image for which the echoimages are adjusted according to the kinds (refer to FIG. 2A) can befinally generated to be displayed on the display module 16.

As described above, the radar indicator 3 includes the reception signalacquiring module 13, the kind identification processing module 18, andthe kind-base signal processing module 20. The reception signalacquiring module 13 acquires the reception signal received by the radarantenna 11. The kind identification processing module 18 identifies thekind of the reception signal. The kind-base signal processing module 20extracts the reception signals for every kind. The kind-base signalprocessing module 20 performs the individual signal processing for everykind of the extracted reception signal.

Thereby, suitable signal processing can be performed according to thekind of the reception signal. Because the reception signal is extractedfor every kind and the individual signal processing is performed, thesignal processing can be prevented from affecting other kinds ofreception signals. Therefore, flexible signal processing is possible,for example, when the gain control is performed as the signalprocessing, only arbitrary kinds of reception signals can be selectivelysuppressed.

In the radar indicator 3 of this embodiment, the kind identificationprocessing module 18 can identify the land, the ship, the buoy (or theflag buoy), the sea surface reflection, and the rain-and-snow clutter asthe kinds of reception signals.

Thus, suitable signal processing according to the kind can be performedby identifying the kind of reception signal based on the origination ofthe echo indicated by the reception signal.

In this embodiment, the radar indicator 3 includes the map informationacquiring module 30 for acquiring the map information. The kindidentification processing module 18 identifies the kind of receptionsignal based on the map information.

Thereby, the kind of reception signal can be identified with sufficientaccuracy based on the map information.

In this embodiment, the radar indicator 3 is configured as follows. Thekind identification processing module 18 identifies the reception signalindicating the land based on the map information. The kind-base signalprocessing module 20 performs signal processing for the reception signalindicating the land, which is different from signal processing for otherkinds of reception signals.

Specifically, because the map information contains the informationindicating at least the position and the shape of the land, thereception signal indicating the land can be identified with sufficientaccuracy based on the map information. Thereby, because the receptionsignal indicating the land can be extracted, the processing peculiar tothe reception signal indicating the land can be performed withoutaffecting other kinds of reception signals.

In this embodiment, the radar indicator 3 includes the AIS informationacquiring module 27 for acquiring the AIS information. The kindidentification processing module 18 identifies the kind of receptionsignal based on the AIS information.

Thereby, the kind of reception signal can be identified with sufficientaccuracy based on the AIS information.

In this embodiment, the radar indicator 3 is configured as follows.Specifically, the kind identification processing module 18 identifiesthe reception signal indicating the ship based on the AIS information.The kind-base signal processing module 20 performs signal processing forthe reception signal indicating the ship, which is different from signalprocessing for other kinds of reception signals.

Because the AIS information contains the information showing theposition of the ship, the reception signal indicating the ship can beidentified with sufficient accuracy based on the AIS information.Thereby, because the reception signal indicating the ship can beextracted, the processing peculiar to the reception signal indicatingthe ship can be performed without affecting other kinds of receptionsignals.

In this embodiment, the radar indicator 3 includes the scan-to-scancorrelation processing module 21 for identifying the reception signalindicating the sea surface reflection. The kind-base signal processingmodule 20 performs signal processing for the reception signal indicatingthe sea surface reflection, which is different from signal processingfor other kinds of reception signals.

Because the reception signal indicating the sea surface reflection canbe extracted, processing peculiar to the reception signal indicating thesea surface reflection can be performed without affecting other kinds ofreception signals.

In this embodiment, the radar indicator 3 includes the statisticalprocessing module 22 for identifying the reception signal indicating therain-and-snow clutter. The kind-base signal processing module 20performs signal processing for the reception signal indicating therain-and-snow clutter, which is different from signal processing forother kinds of reception signals.

Because the reception signal indicating the rain-and-snow clutter can beextracted, processing peculiar to the reception signal indicating therain-and-snow clutter can be performed without affecting other kinds ofreception signals.

In this embodiment, the radar indicator 3 includes the displayprocessing module 15 for synthesizing the reception signals for everykind for which the signal processing is carried out by the kind-basesignal processing module 20 to generate the radar image.

That is, by synthesizing the reception signals for which the signalprocessing is applied according to the kind, the radar image for whichthe echo image is adjusted for every kind can be obtained.

In this embodiment, the radar indicator 3 includes the image memory 31and the display layer selecting module 32. The image memory 31 can storethe reception signals for every kind for which the signal processing iscarried out by the kind-base signal processing module 20, in the layersprepared for every kind. The display layer selecting module 32 selectssome or all layers among the layers for every kind based on the displaylayer selection signals inputted from the exterior. The displayprocessing module 15 synthesizes the layers selected by the displaylayer selecting module 32 to generate the radar image.

Thereby, it is possible by the operator's selection to prevent theunnecessary layer from being displayed.

In this embodiment, the radar indicator 3 includes the header insertionprocessing module 19 for giving the header information according to thekind of the reception signal to the reception signal. The kind-basesignal processing module 20 extracts the reception signals for everykind based on the header information.

Thus, by giving the identifier to the reception signal, the receptionsignal can be easily extracted for every kind by the kind-base signalprocessing module 20.

In this embodiment, the ship radar apparatus 1 includes the antenna unit2 and the radar indicator 3. The antenna unit 2 transmits theelectromagnetic wave and receives the reflection wave to output thereception signal corresponding to the received reflection wave to theradar indicator 3.

The radar apparatus can flexibly perform the signal processing accordingto the kind of the reception signal.

In this embodiment, the signal processing program causes the signalprocessing device to execute processing including the following steps.This signal processing program includes the identifying step, theextracting step, and the kind-base signal processing step. At theidentifying step, the kind of the reception signal received by the radarantenna 11 is identified. At the extracting step, the reception signalis extracted for every kind. At the kind-base signal processing step,the individual signal processing is performed for every kind of theextracted reception signals.

Thereby, suitable signal processing can be performed according to thekind of reception signal. Because the reception signal is extracted forevery kind to perform the individual signal processing, the signalprocessing can be prevented from affecting other kinds of receptionsignals.

One embodiment of the present invention is described above; however, theconfiguration of the embodiment may be modified as follows.

Although the control module 14 is configured with the hardware such asthe CPU, ROM and RAM, and the software such as the program, it may beconfigured with dedicated hardware.

The radar apparatus of this embodiment may be applied to other kinds ofradar apparatuses other than the ship radar apparatus described above.The radar apparatus of this embodiment may also be applied to an FMCWradar other than the pulse-radar-type radar apparatus.

The signal processing device of this embodiment is not limited to theradar indicator provided with the display module. For example, it maynot have the display module but the data of the generated radar imagemay be outputted to an external display.

When generating the radar image by the display processing module 15, theimage processing method at the time of stacking the layers may bechanged by an operator's selection.

For example, when performing the processing for stacking the layers bythe display processing module 15, a transparency of each layer may bespecified by the operator. In this case, if the rain-and-snow clutterlayer is specified to be displayed translucently, the situation in whichit is raining on a ship or a land can be expressed on the radar image.

Further, when performing the processing for stacking the layers by thedisplay processing module 15, a color tone or the like may be specifiedfor each layer by the operator. By configuring in this way, the radarimage can be adjusted even more flexibly, such as displaying a layerwith low importance for the operator in a low-profile color tone, ordisplaying an important layer in a high-profile color tone.

Note that, in the case where the display processing module 15 can adjustthe color tone of the layer as described above, it may be more suitablethat the layer unnecessary for the operator is displayed in thelow-profile color tone. In this case, because the layer containing theunnecessary echo images (for example, sea surface reflection etc.) ismade low in profile, the display layer selecting module 32 may beomitted and all the layers may be outputted to the display processingmodule 15.

By adjusting the color tone of each layer by the display processingmodule 15 as described above, because the specific kind of echo image isdisplayed so as to be emphasized or suppressed, the adjustmentprocessing of the color tone corresponds to the conventional gaincontrol. Therefore, if it is configured so that the color tone of eachlayer can be adjusted as described above, the gain control performed bythe sea surface reflection signal processing module 43 and the like maybe omitted.

In the above embodiment, the header insertion processing module 19 givesthe header information before the reception data is converted from polarcoordinates into rectangular coordinates (that is, before the rasterimage is generated). However, the header information may be given oncethe coordinate conversion is performed. In this case, the headerinformation is given to each pixel of the raster image. In thisconfiguration, the processing by the kind-base signal processing moduleis performed for each pixel of each layer (reception data after beingconverted into the raster images for the kinds).

The identifier given to the reception signal is not limited to the bitflag. The identifier may be any other information which can specify thekind of the reception signal. However, the bit flag may be especiallypreferred as the identifier because it requires fewer data and thecomparison is easy.

The header insertion processing module 19 may be omitted. In this case,for example, a changeover switch for switching a flow of the signal maybe provided between the kind identification processing module 18 and thesignal processing modules 40-44, and the changeover switch may beswitched according to the kind of reception signal. Thereby, thereception signal may be selectively outputted to any of the signalprocessing modules 40-44.

The kinds of reception signal identified by the kind identificationprocessing module 18 are not limited to the examples of the aboveembodiment. For example, without identifying the kind of the targetobject, such as a ship, a buoy, and a flag buoy, the kind may beclassified by a moving speed, such as a moving target object and astationary target object.

Further, the kind identification processing module 18 may identify awhite noise contained in the reception signal. A method of identifyingthe white noise which is a signal other than the reflection echo from areflective object may be as follows. For example, first, a signal levelof reception signals are measured for a time period during which theelectric waves are not transmitted from the radar antenna (time periodduring which the echoes are not received), and the signal levelconcerned is set to a white noise level. If a reception signal below thewhite noise level is detected during a time period during which theechoes are received, the reception signal concerned is identified as thewhite noise.

The method of identifying the kind of reception signal by the kindidentification processing module 18 is not limited to the example of theabove embodiment, but any other suitable method may be used.

For example, because the electronic nautical chart also containspositional information on route buoys, reception signals indicatingechoes from the route buoys may be identified based on the chartinformation. Further, for example, in order to identify an echo from amoving target object such as a ship, the information on a trail (trace)may be used. Further, for example, in order to identify echoes based onrain-and-snow clutters, weather information from a satellite radiostation may be used. Further, by performing complex signal processingfor the reception signal, the kind of the reception signal may beidentified based on information on a phase and a frequency which areacquired.

The signal processing performed by the signal processing modules 40-44are not limited to the examples of the above embodiment, but may be anyother signal processing.

For example, the rain-and-snow clutter signal processing module 44 mayperform TT (Target Tracking) Because only the reception data indicatingthe rain-and-snow clutters can be extracted by the configuration of theabove embodiment, the TT for the rain-and-snow clutters becomespossible. Note that the TT is a technique in which a course of a targetobject is predicted by acquiring and tracking the target object on theradar image. Thereby, a ship can travel on the course avoiding rain,while predicting the moving direction and the like of rain clouds.

Further, for example, the ship signal processing module 41 may performecho trail generation processing. Thereby, because a trail (trace) isgenerated only for the echo image indicating a ship and the trail is notgenerated for the sea surface reflections, the trail can be clearlydisplayed.

The ship signal processing module 41 may not perform any signalprocessing. Because the configuration of the above embodiment cansuppress only the unnecessary signals without suppressing the receptionsignals indicating the echoes from ships. Therefore, even if it does notperform processing in particular for emphasizing the reception signalsindicating the ships, the operator is able to recognize the echo imagesof the ships easily on the radar image.

Further, for example, the ship signal processing module 41 may performprocessing for displaying a mark of a ship at a position where the shipexists.

What kind of signal processing is to be carried out for a kind of thereception signal may vary with the application of the apparatus,preferences of the operator, weather conditions, situations ofsurrounding target objects, etc. Therefore, it may be preferred that thesignal processing by the kind-base signal processing module 20 can beset and changed by the operator, depending on the kind of receptionsignal. Thereby, the signal processing can be performed flexiblyaccording to the needs of the operator, if needed.

In the foregoing specification, specific embodiments of the presentinvention have been described. However, one of ordinary skill in thetechnique appreciates that various modifications and changes can beperformed without departing from the scope of the present invention asset forth in the claims below. Accordingly, the specification andfigures are to be regarded in an illustrative rather than a restrictivesense, and all such modifications are intended to be included within thescope of present invention. The benefits, advantages, solutions toproblems, and any element(s) that may cause any benefit, advantage, orsolution to occur or become more pronounced are not to be construed as acritical, required, or essential features or elements of any or all theclaims. The invention is defined solely by the appended claims includingany amendments made during the pendency of this application and allequivalents of those claims as issued.

Moreover in this document, relational terms such as first and second,top and bottom, and the like may be used solely to distinguish oneentity or action from another entity or action without necessarilyrequiring or implying any actual such relationship or order between suchentities or actions. The terms “comprises,” “comprising,” “has,”“having,” “includes,” “including,” “contains,” “containing” or any othervariation thereof, are intended to cover a non-exclusive inclusion, suchthat a process, method, article, or apparatus that comprises, has,includes, contains a list of elements does not include only thoseelements but may include other elements not expressly listed or inherentto such process, method, article, or apparatus. An element proceeded by“comprises . . . a,” “has . . . a,” “includes . . . a,” “contains . . .a” does not, without more constraints, preclude the existence ofadditional identical elements in the process, method, article, orapparatus that comprises, has, includes, contains the element. The terms“a” and “an” are defined as one or more unless explicitly statedotherwise herein. The terms “substantially,” “essentially,”“approximately,” “about” or any other version thereof, are defined asbeing close to as understood by one of ordinary skill in the technique,and in one non-limiting embodiment the term is defined to be within 10%,in another embodiment within 5%, in another embodiment within 1% and inanother embodiment within 0.5%. The term “coupled” as used herein isdefined as connected, although not necessarily directly and notnecessarily mechanically. A device or structure that is “configured” ina certain way is configured in at least that way, but may also beconfigured in ways that are not listed.

What is claimed is:
 1. A display device, comprising: a reception signal acquiring module for acquiring reception signals received by a radar antenna during a single antenna scan; an identifying module for identifying a target kind of each reception signal; an extracting module for extracting the reception signal for each identified target kind; a layer storage that stores the extracted reception signals such that each extracted reception signal is associated with a layer according to the identified target kind, each layer being associated with a particular target kind; a display layer selector for selecting at least one layer for display; and a display processor for generating an individual radar image for each of the selected at least one layer such that each generated individual radar image corresponds to an identified target kind, and for displaying the generated individual radar image corresponding to the selected at least one layer.
 2. The display device of claim 1, wherein the identifying module identifies at least any one of the target kinds associated with the reception signal, the target kinds including a land, a ship, a buoy, a flag buoy, a sea surface reflection, a rain-and-snow clutter, and a white noise.
 3. The display device of claim 1, further comprising a map information acquiring module for acquiring map information; wherein the identifying module identifies the target kind of the reception signal based on the map information.
 4. The display device of claims 1, further comprising an AIS information acquiring module for acquiring AIS information; wherein the identifying module identifies the target kind of the reception signal based on the AIS information.
 5. The display device of claims 1, wherein the identifying module identifies the reception signal indicating a sea surface reflection target kind.
 6. The display device of claims 1, wherein the identifying module identifies the reception signal indicating a rain-and-snow clutter target kind.
 7. The display device of claim 1, the display processor synthesizing each generated individual radar image corresponding to each selected layer to generate a displayed radar image based on the synthesized individual radar images.
 8. The display device of claim 1, displaying the generated individual radar image comprising: performing individual image processing for each generated individual radar image corresponding to a selected layer based on the target kind of the selected layer, the individual image processing including enhancing or suppressing or adjusting one or more of a transparency and a color tone of the individual radar image based on the target kind of the selected layer.
 9. The display device of claim 8, performing individual image processing for each generated individual radar image including suppressing the individual radar image associated with a rain-and-snow clutter target kind or a white noise target kind or a sea surface reflection target kind.
 10. The display device of claim 8, performing individual image processing for each generated individual radar image including enhancing the individual radar image associated with a ship target kind or a land target kind.
 11. The display device of claim 5, further comprising: a kind-based signal processor for performing sea surface reflection signal processing for an extracted reception signal identified as a sea surface reflection target kind, said sea surface reflection signal processing being different from signal processing for other target kinds.
 12. The display device of claim 6, further comprising: a kind-based signal processor for performing rain-and-snow clutter signal processing for an extracted reception signal identified as a rain-and-snow clutter target kind, said rain-and-snow clutter signal processing being different from signal processing for other target kinds.
 13. The display device of claim 1, where: the display layer selector selects at least two layers for display; and the display processor generates an individual radar image for each of the selected at least two layers such that each generated individual radar image corresponds to an identified target kind.
 14. A method, comprising: acquiring reception signals received by a radar antenna during a single antenna scan; identifying a target kind of each acquired reception signal; extracting the reception signal for each identified target kind; storing the extracted reception signals in a storage such that each extracted reception signal is associated with a layer according to the identified target kind, each layer being associated with a particular target kind; selecting at least one stored layer for display; generating an individual radar image for each of the selected at least one layer such that each generated individual radar image corresponds to an identified target kind, and displaying the generated individual radar image corresponding to the selected at least one layer.
 15. The method of claim 14, the method further comprising: performing a kind-based signal processing for an extracted reception signal based on the target kind, said kind-based signal processing being different from signal processing for other target kinds.
 16. The method of claim 14, the method further comprising: synthesizing each generated individual radar image corresponding to each selected layer to generate a displayed radar image based on the synthesized individual radar images.
 17. The method of claim 14, displaying the generated individual radar images comprising: performing individual image processing for each generated individual radar image corresponding to a selected layer based on the target kind of the selected layer, the step of performing individual image processing including enhancing or suppressing or adjusting one or more of a transparency and a color tone of the individual radar image based on the target kind of the selected layer.
 18. The method of claim 17, performing individual image processing for each generated individual radar image including suppressing the individual radar image associated with a rain-and-snow clutter target kind or a white noise target kind or a sea surface reflection target kind.
 19. The method of claim 17, performing individual image processing for each generated individual radar image including enhancing the individual radar image associated with a ship target kind or a land target kind.
 20. The method of claim 14, said selecting including selecting at least two layers for display; and generating an individual radar image including generating an individual radar image for each of the selected at least two layers such that each generated individual radar image corresponds to an identified target kind.
 21. The method of claim 17, where each of the steps of enhancing, suppressing, and adjusting one or more of a transparency and a color tone of the individual radar image are performed based on an indication of importance associated with the selected layer. 